1. Field of the Disclosure
The present disclosure relates to xerographic printers, and specifically to a mechanism which ensures that an exit window of a raster output scanner is simultaneously cleaned as a developer customer replacement unit of a printing apparatus is replaced.
2. Description of Related Art
Typically, in the process of electrostatographic or xerographic printing, an electrostatic latent image is formed on a charge-retentive surface, and then developed with an application of toner particles. The toner particles adhere electrostatically to the suitably-charged portions of the imaging surface. The toner particles are then transferred, by the application of electric charge, to a print sheet, forming the desired image on the print sheet. An electric charge can also be used to separate or “detack” the print sheet from the imaging surface. For machines using an electrostatic brush cleaner, a preclean electric charge is used to adjust the charge on toner particles entering the electrically biased cleaning brush. In some multiple color machines, e.g., a single pass image-on-image system, electric charge is used to recharge the toner and photoreceptor from the previous development step prior to development of the next color. In tandem multiple color machines using development to an intermediate surface, electric charge is used for first transfer from each photoreceptor to the intermediate and for second transfer from the intermediate to paper. One such printer is shown in U.S. Pat. No. 5,689,769 and it and the references cited therein are incorporated herein by reference to the extent necessary to practice the present disclosure.
In printing machines such as the one described above, a CRU is a customer replacement unit which can be replaced by a customer at the end of life or at the premature failure of one or more of the xerographic components. The CRU concept integrates various subsystems whose useful lives are predetermined to be generally the same length. The service replacement interval of the CRU ensures maximum reliability and greatly minimizes unscheduled maintenance service calls. Utilization of such a strategy, allows customers to participate in the maintenance and service of their copier/printers. CRUs ensure maximum up time of copier/printers and minimize down time and service cost due to end of life or premature failures.
It is important that customer replacement units be customer friendly. That is, it is important that the CRUs may be easily removed and reinstalled with minimal instructions and minimal training. Unfortunately, the CRUs typically include a number of items that are critical to the proper operation of the machine, e.g., charging devices, photoreceptors and toner cleaner subsystems and other subsystems. The components and subsystems are very delicate and need to be properly handled and not damaged during the installation and removal of the CRUs.
Among many types of light exposure systems in printers is the commonly used raster output scanner (ROS). A raster output scanner is comprised of a laser beam source, a modulator for modulating the laser beam (which, as in the case of a laser diode, may be the source itself), such that the laser beam contains information that is to be created, a rotating polygon having at least one reflective surface, input optics that collimate the laser beam, output optics which focus the laser beam into a spot on a photoreceptor's surface and which corrects for various optical problems, such as, wobble and usually one or more folding mirrors. The laser source, modulator, and input optics produce a collimated laser beam which is directed toward the polygon. As the polygon rotates, the reflective surface(s) causes the laser beam to be swept along a scan plane. The swept laser beam passes though the output optics and is reflected by the mirror(s) so as to produce a sweeping spot on the charged photoreceptor and which traces a scan line across the photoreceptor. Since the charged photoreceptor moves in a direction which is substantially perpendicular to the scan line, the sweeping spot raster scans the photoreceptor. By suitably modulating the laser beam as the spot raster scans the photoreceptor a desired latent image can be produced on the photoreceptor.
The ROS is usually enclosed in a compartment to protect it from contaminants. In that case, the enclosed compartment has an exit window, a glass window disposed between the ROS and the photoreceptor, through which the laser beam can pass. While the inclusion of an exit window reduces contamination of the ROS itself, the mobile natures of the contamination combined with the turbulent air flow around a moving photoreceptor, means that if left alone the exit window aperture will eventually become coated with contaminants.
In the prior art, to prevent the exit window from being excessively contaminated, field service personnel were instructed to clean the exit window at every service call. This was not thoroughly satisfactory since the service provider could fail to clean the exit window, or if the machine does not require frequent service, excessive contamination could result. While a fully automated exit window cleaner could be implemented, its cost would be excessive, especially, in low cost machines.
Additionally, state of the art laser image developers consist of an expendable developer cartridge that contaminates the aperture when it slides in and out of a laser printer when the need arises for it be replaced or otherwise serviced. During the time in which the unit is in service in the printer, waste toner is removed via a mechanical connection within the body of the printer. Waste toner may also accumulate around the surfaces of the cartridge during use. Toner may also accumulate on the surfaces around the cartridge due to leakage or normal migration of toner particles. One of these surfaces is the aperture through which the laser beam, which writes the image, travels to the photosensitive drum. This surface typically is a plate of optical quality glass. In many cases, this plate lies beneath the developer cartridge and lies in a horizontal orientation. It is known in the art that toner may accumulate on this aperture and appropriate measures are taken to provide for cleaning. This method is typically a wand with a cleaning pad attached to one end that can be inserted into the space between the developer and the aperture. This is done when image quality problems are noticed that may corrected by this procedure. Two problems arise that must be addressed at times using this method.
First is the slow accumulation of toner on the aperture that may go unnoticed and simply degrade the image quality over time. The customer may not notice the degradation over time and unknowingly accept lower than optimum print quality. Secondly is the obvious problem of toner dropping from the developer unit when it is removed and/or replaced and causing noticeable image quality problems that may or may not be recognized as being caused by toner on the aperture. These problems can mistakenly be blamed on the quality of the imaging unit and have resulted in calls to a service center.
Hence, the need still exists for a low cost ROS exit window cleaner.